The present disclosure relates to biocompatible devices and coatings.
Implantable prostheses are increasingly being utilized in orthopedics to treat degenerative diseases and traumatic fractures. These include hip and joint replacements as well as the internal fixation of fractures. Similarly, dental implants are increasingly being utilized in dentistry to treat missing, diseased and damaged dentitions. However, the long-term retention and functionality of these implants is dependent on their biocompatibility and their integration into the surrounding tissues. Indeed, despite some biocompatibility of certain currently available implants, the biological response can be inadequate and tissue integration compromised.
The currently available implants are dominated by titanium and titanium alloys because of their physical and mechanical properties and biocompatibility. This biocompatibility is characterized by a general biological inertness that leads to the formation of a mechanical bond with the surrounding tissues. However, in the unmodified state their lack of bioactivity can restrict their tissue integration.
To improve their biocompatibility and expand their bioactivity, titanium implant surfaces have been subject to a range of surface modifications and enhancements. These modifications include: (1) enhanced surface topography and roughness through mechanical and micro-machining methods, plasma spraying, sandblasting and the application of surface coatings; (2) improved corrosion resistance through surface coatings; and (3) enhanced bioactivity through surface oxidation and coatings.
Among these various implant surface modification techniques, the plasma spraying technology is well developed and most commonly used. In this technique, powder materials melt in an ultra-high temperature plasma flame and the coating rapidly solidifies under high-speed airflow. Although the plasma spraying process is fast, uniform, repeatable and suitable for industrial production, it is an expensive process that is not suitable for coating porous metal surfaces. Moreover, the coatings are not strongly adherent to the implants and have poor long-term durability.
Other approaches to improve the biocompatibility of implant surfaces include surface oxidation and modification by an alkali treatment, and the addition of calcium phosphate coatings onto oxidized titanium surfaces. In such a process, the surface is initially activated in its metal oxide layer, and a coating then deposited with bioactive materials. The resultant bioactive metal oxide composite coatings may exhibit enhanced tissue integration and resistance to corrosion. More recently, polymeric materials have been increasingly evaluated for their application as implantable biomaterials. Polymeric substrates have been further modified and coated with titania to enhance their biocompatibility. These modifications have included sputter-coating, vapor deposition and plasma spraying for the application of titanium and other metals to enhance the cellular response. Additionally, recent studies have utilized nanoscale TiO2 coatings to further enhance the cellular response. Therefore, polymeric surfaces have been further coated and augmented with nano-features by different techniques including ionic plasma deposition, nitrogen ion immersion plasma deposition, and physical vapour deposition.
Unfortunately, the aforementioned complex processes often involve multi-step techniques, typically require stringent conditions that limit product performance, and can require solution-phase processing with costly and potentially harmful solvents. Furthermore, in the case of coatings that involve multiple layers, the interface that lies between adjacent surface modifications may be weak and susceptible to failure.